Tumors of cartilaginous origin represent one of the largest categories of skeletal neoplasms. Here, the authors will review basic cartilage biology and the MR imaging characteristics of the most common benign and malignant neoplasms that contain hyaline cartilage.
Tumors of cartilaginous origin represent one of the largest
categories of skeletal neoplasms. It is a heterogeneous group of
benign and malignant tumors composed either of pure cartilage or
cartilage in combination with various amounts of myxoid, fibrous,
or osseous tissue. Conventional radiography remains instrumental in
the diagnosis of cartilaginous and other primary skeletal
neoplasms. It provides the best opportunity to characterize the
lesion and gives an initial assessment of tumor aggressiveness,
size, and extent. In addition, computed tomography (CT) may detect
subtle calcifications not visible on plain radiographs, and
magnetic resonance (MR) imaging provides definitive local staging.
MR's multiplanar imaging capability and superior soft-tissue
contrast, compared to CT, allows for accurate evaluation of tumor
invasion into adjacent muscles and neurovascular bundles. The
extent of bone marrow involvement also is more reliably identified
with MR than CT.
Considerable overlap exists in the MR appearance of
histologically unrelated lesions. Most malignant tumors demonstrate
low to intermediate signal intensity on T1-weighted (T1W) images,
high signal intensity on T2-weighted (T2W) images, and marked
enhancement following intravenous injection of gadolinium. Benign
and low grade malignant tumors containing hyaline cartilage have a
similar pattern but demonstrate unique characteristics that easily
distinguish them from non-hyaline cartilage-containing tumors.1
This article will review basic cartilage biology and the MR imaging
characteristics of the most common benign and malignant neoplasms
that contain hyaline cartilage.
A basic knowledge of the different types and distribution of
cartilage within the musculoskeletal system provides an insight
into the imaging characteristics and location of hyaline
cartilage-containing tumors. Hyaline cartilage and fibrocartilage
are the two basic types found in the musculoskeletal system. They
both are connective tissue of mesenchymal origin, characterized by
a firm consistency and hypovascularity. Fibrocartilage is the
primary constituent of synchondroses, symphyses, and menisci.
Hyaline cartilage is a critical component of skeletogenesis; it
also is found in physes, and it lines the articular surface of
The vast majority of the skeleton passes through an intermediate
cartilage step during formation, a process termed enchondral
ossification. The clavicle, mandible, and craniofacial bones are
exceptions, as these undergo a different process called
intramembranous ossification. The distribution of hyaline
cartilage-containing tumors is greatly influenced by the process of
ossification, with most lesions occurring in bones that are formed
through enchondral ossification.
The structural differences between hyaline and fibrocartilage
account for their different appearance on MR imaging. Compared to
fibrocartilage, hyaline cartilage contains less collagen and more
proteoglycan. The higher proteoglycan content results in higher
water content. Fibrocartilage contains more collagen and less
proteoglycan, therefore containing less water. On T2W images,
hyaline cartilage characteristically demonstrates homogeneous
increased signal intensity while fibrocartilage shows decreased
signal intensity. Within tumors, hyaline cartilage grows in a
lobular pattern, with or without fibrous septa, that can easily be
seen on MR imaging. It may contain rings, arcs, or punctate areas
of calcification that are detectable on conventional radiography,
tomography, CT, or MR imaging.
Hyaline cartilage-containing tumors include osteochondroma,
enchondroma, parosteal chondroma, low grade chondrosarcoma,
chondroid chordoma, and chondroblastic osteosarcoma. Myxoid and
chondroid are other types of cartilage encountered in these
neoplasms. Myxoid cartilage is a variant of hyaline cartilage,
contains prominent cystic cavities, and can be seen in some hyaline
cartilage-containing tumors including chondrosarcoma, enchondroma,
and parosteal chondroma. Chondroid refers to a primitive form of
fibrocartilage and is typically associated with chondro-blastoma,
chondromyxoid fibroma, mesenchymal chondrosarcoma, and certain
Hyaline cartilage-containing tumors
Osteochondroma-Osteochondromas are the most common benign
cartilage-containing tumor.2,3 These heterogeneous tumors are
composed of trabecular bone and marrow, are surrounded by a thin
cortex, and are covered by a hyaline cartilage cap over the outer
surface. The thickness of the hyaline cartilage is variable and
dependent upon the degree of skeletal maturation and malignant
transformation. Osteochondromas typically are located in the
metaphyseal region of long bones and are connected to the host bone
by either a broad base (sessile) or a narrow stalk (pedunculated).
Osteochondromas most likely arise at the physeal periphery from
reorientation of a physeal fragment, congenital perichondral
deficiency or, rarely, following radiation.3,5
Osteochondromas may be discovered as an incidental finding or
may present with nonspecific signs and symptoms, including a mass
with or without pain, skeletal deformity, or pain caused by
compression of adjacent neurologic structures. Complications
include fracture through the osteochondroma, repetitive trauma to
adjacent structures, and malignant transformation. The risk of
malignant transformation of an isolated osteochondroma is
approximately 1%. Malignancy should be suspected if there is growth
of the osteochondroma after skeletal maturity or the thickness of
the hyaline cartilage cap exceeds 2 to 3 cm. Malignant
transformation typically results in low grade chondrosarcomas,
although higher grade lesions are possible.6 If malignant
transformation occurs, it usually is present in lytic regions or
areas of bulky unmineralized cartilage.
Diagnosis of osteochondroma can be readily made with
conventional radiography and rests upon demonstrating continuity of
the host bone marrow cavity and cortex with that of the
osteochondroma. The lesion can easily be identified as arising from
the surface of bone pointing away from an adjacent joint. The
lobular growth pattern of hyaline cartilage is recognized by the
bulbous or lobular gross morphologic appearance to the end of the
osteochondroma. However, the extent and pattern of mineralization
within the hyaline cartilage can be overlooked at MR, though it is
well demonstrated on CT. This degree of mineralization varies with
cap thickness, and MR has been found to be superior in assessment
of hyaline cartilage cap thickness and demonstration of the
relationship of adjacent structures (figure 1). The cap typically
is only several millimeters thick and will demonstrate low to
intermediate signal intensity on T1W images, high signal intensity
on T2W images, and no
or slight peripheral enhancement following intravenous injection
of gadolinium.7 Both MR and CT display equally well the continuity
of the osteochondroma marrow and cortex with that of the parent
The risk of malignant transformation is higher in patients with
hereditary multiple osteochondromatosis (15 to 20%). This disorder
is transmitted as an autosomal dominant trait and results in
multiple sessile and pedunculated osteochondromas distributed in a
bilateral symmetric pattern. The polyostotic metaphyseal
involvement can result in marked growth disturbances.
Enchondroma-Enchondromas are the second most common
cartilage-containing neoplasms and, unlike osteochondromas, are
composed of pure hyaline cartilage.2,3 They are benign, usually
solitary intramedullary tumors which most likely arise from the
physis as dysplastic, hypercellular hyaline cartilage nodules.8
Enchondromas even-tually separate themselves from the physis and
reside within the metaphysis. This process may be of variable
duration, resulting in enchondromas of variable size. A widespread,
long-standing process could explain the abnormalities encountered
in Ollier's disease, while a limited, localized process would
result in a solitary enchondroma.
Enchondromas often are discovered incidentally or following
pathologic fracture. Although pain associated with long bone
enchondromas may be due to secondary chondrosarcoma, it must be
distinguished from a pathologic fracture or adjacent joint or
soft-tissue abnormality. Malignant transformation is a more
worrisome complication of enchondroma. The age of the patient and
duration of symptoms are important clues in determining the
likelihood of malignant transformation. An adult patient with
gradually increasing pain over a long duration in the region of a
presumed enchondroma should be seriously considered to have a
The distribution and radiographic appearance of enchondromas
have been well described. They typically are centrally located
within the medullary canal and have a predilection for the short
tubular bones, proximal femur, and proximal humerus. Enchondromas
usually are metaphyseal in location and demonstrate geographic
destruction with a lobulated contour. There may be a variable
amount of mineralization present, which would appear as small,
punctate ring or arc-like densities and reflect dystrophic
calcifications within small cartilage nodules or fragments of
lamellar bone that encase the nodules. Focal areas of cortical
endosteal scalloping also may be present. If the enchondroma arises
within a small tubular bone (such as the phalanx, rib, or fibula),
the bone may show expansion due to its small size.
MR of enchondroma shows low to intermediate signal intensity on
T1W and prominent areas of high signal intensity on T2W images. CT
and MR both are superior to conventional radiography for
visualizing cortical destruction and associated soft-tissue mass,
both ominous signs that indicate malignant transformation. Matrix
calcifications identified on MR imaging are depicted as low signal
intensity foci and are more apparent on gradient echo sequences.
Normal marrow fat may be present interspersed between the cartilage
nodules, a finding that indicates benignancy (figure 2). The use of
intravenous gadolinium may be useful in distinguishing enchondromas
from low grade chondrosarcomas;9,10 enchondromas typically show a
peripheral enhancement pattern while chondrosarcomas demonstrate a
septal enhancement pattern.
Chondrosarcoma-Chondrosarcomas are classified according to their
site of origin and presence of a prior lesion. These tumors are
termed central if they arise within the medullary canal, peripheral
or exostotic if they arise from an osteochondroma, and
juxtacortical if they arise from the surface of bone.
Chondrosarcomas also are divided into primary or secondary
categories, based upon the absence or presence of a preexisting
lesion. Conventional chondrosarcomas are easily classified using
these criteria. Nonconventional chondrosarcomas, however, require
additional categories that reflect their unique pathologic
features. This group includes dedifferentiated, mesenchymal, clear
cell, and extraskeletal chondrosarcomas (table 1).
The majority of chondrosarcomas are central (either primary or
secondary) or peripheral. As a group, they are slow growing, low
grade lesions. Patients typically present with a history of
gradually increasing pain which is often worse at night. Local
swelling or a palpable mass may be present. These symptoms may be
present for many years prior to diagnosis.
Conventional chondrosarcomas generally are composed of a single
confluent mass of malignant hyaline to myxoid containing cartilage.
Grossly, they have a lobular morphology, reflecting the growth
pattern of cartilage with variable amounts of calcification.
Diagnosis of low grade tumors may be difficult based upon cytologic
criteria alone. Low grade tumors are cytologically bland, lacking
distinguishing features from cellular (atypical) enchondromas.
However, the presence of fibrous bands at the tumor-marrow
interface has been used as a criterion to separate low grade
chondrosarcomas from atypical enchondromas.11 Other criteria used
in the diagnosis of malignancy include cortical thickening due to
invasion of the haversian system and cortical erosion with or
without associated soft-tissue mass.8 In comparison, high grade
tumors show cellular anaplasia, allowing diagnosis by standard
Radiographic features of chondrosarcoma reflect the gross
morphology and mineralization of the cartilage malignancy. Low
grade chondrosarcomas may have a deceiving non-aggressive
appearance on conventional radiography. Fortunately, most tumors
are typically large, with a lobular appearance due to their slow
growth rate pattern. Central lesions can demonstrate predominately
lytic destruction, cortical thickening, broad areas of cortical
scalloping, symmetric expansion of bone, and minimal calcification,
with or without an associated soft-tissue mass. CT easily
demonstrates the cortical changes and characterizes the
mineralization, and MR reveals hyperintense signal intensity on T2W
images due to the rich water content within the hyaline
cartilage-containing lobules. Decreased signal intensity present on
these images corresponds to intervening fibrous septa or
calcification. Enhancement of the fibrous septa separating the
cartilage lobules is evident following intravenous gadolinium and
can be a useful finding in distinguishing between benign and low
grade malignant cartilage tumors.9,10 Secondary peripheral or
exostotic chondrosarcomas demonstrate similar radiographic
appearances, though they lack alterations of the host bone. High
grade neoplasms appear less lobulated, with more necrosis and loss
of the septal enhancement pattern. Fortunately, these lesions are
not difficult to diagnose histologically.
Approximately 10% of primary and secondary chondrosarcomas
dedifferentiate into more anaplastic high grade sarcomas
(dedifferentiated chondrosarcoma). Dedifferentiation can be seen
with both low and high grade chondrosarcomas. It is defined
histologically by the presence of high grade malignant tissue
juxtaposed to chondrosarcoma. Radiographically, the transition is
apparent. A more aggressive pattern of bone destruction may be
identified, permeative or moth-eaten, with cortical destruction and
soft-tissue mass. There is a poorer prognosis with higher incidence
of metastasis similar to high grade sarcomas.
Chondrosarcoma cells do not require a vascular supply and can
easily be transplanted. Any cells deposited within the surgical
field are likely to result in a local recurrence (figure 5). Great
care must be taken when treating chondrosarcomas that the surgical
site and bone graft donor site are not contaminated with cartilage
Knowledge of the types and distribution of cartilage provides a
foundation for understanding the imaging characteristics and
location of hyaline cartilage-containing tumors. These tumors have
a characteristic appearance on MR imaging. Differentiation between
enchondromas and low grade chondrosarcomas can be difficult when
based only on histologic findings. Correlation with the imaging
appearance can be extremely helpful in arriving at a correct
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Dr. Walker and Dr. Moore are Associate Professors in the
Department of Radiology at the University of Nebraska Medical
Center in Omaha.